The present invention relates to a device and a method for growing a semiconductor thin film by means of liquid-phase epitaxial growth on a semiconductor substrate, and more particularly to a device and a method for thin film epitaxial growth which enables a multi-layer thin film epitaxy on a substrate.
Epitaxy has taken importance as a manufacturing method for multi-layer thin film epitaxial layers of compound semiconductors such as Gallium Phosphide, GaP, Gallium Arsenide, GaAs, Indium Phosphide, InP, etc. for which slide processing has been widely used in the field. FIG. 1A shows schematically a cross-sectional diagram of an epitaxial growth system making use of the slide processing method as a typical example of liquid-phase epitaxy of prior art, and FIG. 1B shows the temperature distribution within an electric furnace.
Hereinafter, the liquid-phase epitaxy of prior art will be briefly described with its basic configuration, referring to an embodiment of Gallium Arsenide (GaAs). A boat shown in the FIG. 1A includes a movable substrate holder 3 which maintains substrates 5 and 6, a first melting liquid holder 7, a second melting liquid holder 8 on the substrate holder and a supporting plate 4 for the melting liquid holders. In case of growing a thin film gallium arsenide mixed compounds on the gallium arsenide substrate 5, metal substances and impurities are added in the melting liquid holders 7 and 8 in order to attain a thin-film epitaxial layer having a mixed crystal ratio, a conductivity type and an electric charge density which are prescribed. Then, in considering a configuration of growing P-type gallium aluminum arsenide GaAlAs on a P-type GaAs substrate for use in a light emitting diode (LED) and also growing N-type GaAs on the P-type GaAlAs, gallium (Ga) is used as a primary solvent material to which GaAs, Al and zinc (Zn) are added in a first melting liquid 9, and GaAs and tellurium (Te) are added in a second melting liquid 10. In the initial stage, the boat in which the substrate 5 rests is out of contact with the Ga melting liquid 9 and 10 and is inserted into a quartz tube 2 filled with the hydrogen ambient. The electric furnace 1 is driven to heat so that the temperature within the epitaxy system is invariably kept up in a range of 750.degree. C. to 900.degree. C. independent of any alteration of positions within the system, as illustrated in the temperature distribution diagram of FIG. 1B. By this heating the metal substances and impurities added to the Ga melting liquid 9 and 10 get melted enough. After enough melting of the metal substances and the impurities, the substrate holder 3 is slid out and the first melting liquid 9 comes to be in contact with the substrate 5. Then, as the temperature goes down slowly, a first-layer GaAlAs thin-film epitaxial growth is made. The substrate holder is again slid out and the second melting liquid 10 comes to be in contact with the substrate 5. By continuously decreasing the temperature, a second GaAs layer is grown in epitaxy. Termination of epitaxial growth can be made through sliding out the substrate holder 3 and mechanically removing the melting liquid 10 out of the substrate 5. The feature in the slide processing is to make thin-film epitaxial layers of different quality grow in sequence by using a plurality of melting liquids. However, in case that the first substrate 5 and the second substrate 6 are set in the holder 3 and the epitaxial growth of the two substrates is continuously made with said liquid-phase epitaxy, the temperature of the epitaxy system must be decreased during growth is the thin-film epitaxy by having the first substrate 5 be in contact with the first melting liquid 9. After the epitaxial growth of a first layer finishes, the first substrate 5 gets in touch with the second melting liquid 10 by means of sliding out the substrate holder and, at the same time, the second substrate 6 touches the first melting liquid 9. Because the second substrate 6 becomes to be in contact with the first melting liquid 9 under the environment of a temperature different from the temperature in the first layer epitaxy of the first substrate, a thin-film of very different quality from the first layer on the first substrate is formed in a first layer of the second substrate. Accordingly, the continuous epitaxial growths cannot be made in equal condition and on a plurality of substrates by means of the prior liquid-phase epitaxy. This fact lowers the yields of chips and also increases waste of raw material such as gallium. In addition to that, when ambient temperature is up to the growing temperature and is continuously kept up so that the material in the molten gallium is made into an saturated enough solution, the surfaces of the substrates are exposed to the hydrogen ambient of high temperature. By this reason, a heat dissolution reaction arises on the surface of the substrates and thereby it frequently results in an arsenic vacancy defect at the surface of the substrates.